Plasmonic photocathode emitters at ultraviolet and visible wavelengths

Abstract

A photocathode emitter can include a transparent substrate, a photocathode layer, and a plasmonic structure array disposed between the transparent substrate and the photocathode layer. The plasmonic structure can serve as a spot-confining structure and an electrical underlayer for biasing the photocathode. The plasmonic structure can confine the incident light at subwavelength sizes.

What is claimed is: 
     
       1. A photocathode emitter comprising:
 a transparent substrate; 
 a photocathode layer; 
 a plasmonic structure array disposed between the transparent substrate and the photocathode layer; and 
 a cap layer disposed on a side of the photocathode layer opposite the plasmonic structure array, wherein the cap layer includes ruthenium. 
 
     
     
       2. The photocathode emitter of  claim 1 , wherein the photocathode layer includes one or more of GaN, an alloy of Al(In)GaN(P), Cs(K)Te(Sb), CsI, or CsBr. 
     
     
       3. The photocathode emitter of  claim 1 , wherein the transparent substrate includes one or more of ultraviolet fused silica, CaF 2 , quartz, sapphire, MgF 2 , or LiF. 
     
     
       4. The photocathode emitter of  claim 1 , wherein the plasmonic structure includes an array of a metallic material. 
     
     
       5. The photocathode emitter of  claim 4 , wherein the metallic material is aluminum. 
     
     
       6. The photocathode emitter of  claim 1 , further comprising a layer between the plasmonic structure array and the photocathode layer, wherein the layer provides lattice matching between the plasmonic structure array and the photocathode layer. 
     
     
       7. A method comprising:
 providing a photocathode, wherein the photocathode includes:
 a transparent substrate; 
 a photocathode layer; 
 a plasmonic structure array disposed between the transparent substrate and the photocathode layer; and 
 a cap layer disposed on a side of the photocathode layer opposite the plasmonic structure array, wherein the cap layer includes ruthenium 
 
 directing a beam of light at the photocathode; and 
 generating a beam of electrons from the photocathode. 
 
     
     
       8. The method of  claim 7 , wherein the plasmonic structure includes an array of a metallic material. 
     
     
       9. The method of  claim 7 , wherein the photocathode further includes a layer between the plasmonic structure array and the photocathode layer, wherein the layer provides lattice matching between the plasmonic structure array and the photocathode layer. 
     
     
       10. A photocathode emitter comprising:
 a transparent substrate; 
 a photocathode layer; 
 a plasmonic structure array disposed between the transparent substrate and the photocathode layer; and 
 a doped wide bandgap semiconductor layer disposed on the plasmonic structure array opposite the photocathode layer. 
 
     
     
       11. The photocathode emitter of  claim 10 , wherein the transparent substrate includes one or more of ultraviolet fused silica, CaF 2 , quartz, sapphire, MgF 2 , or LiF. 
     
     
       12. The photocathode emitter of  claim 10 , wherein the photocathode layer includes a negative electron affinity or a positive electron affinity material. 
     
     
       13. The photocathode emitter of  claim 12 , wherein the photocathode layer includes one or more of Cs, CsBr, CsI, Ba, BaO, or Ba on a refractory oxide. 
     
     
       14. The photocathode emitter of  claim 10 , wherein the doped wide bandgap semiconductor layer includes a dopant, wherein the dopant is at least one of molybdenum or tungsten. 
     
     
       15. The photocathode emitter of  claim 10 , wherein the plasmonic structure defines a plurality of plasmonic cavities. 
     
     
       16. A photocathode emitter comprising:
 a transparent substrate; 
 a photocathode layer; 
 a plasmonic structure array disposed between the transparent substrate and the photocathode layer; and 
 a layer between the plasmonic structure array and the photocathode layer, wherein the layer provides lattice matching between the plasmonic structure array and the photocathode layer. 
 
     
     
       17. The photocathode emitter of  claim 16 , wherein the photocathode layer includes one or more of GaN, an alloy of Al(In)GaN(P), Cs(K)Te(Sb), CsI, or CsBr. 
     
     
       18. The photocathode emitter of  claim 16 , wherein the transparent substrate includes one or more of ultraviolet fused silica, CaF 2 , quartz, sapphire, MgF 2 , or LiF. 
     
     
       19. The photocathode emitter of  claim 16 , wherein the plasmonic structure includes an array of a metallic material. 
     
     
       20. The photocathode emitter of  claim 19 , wherein the metallic material is aluminum.